Radiation-curable aqueous dispersions

ABSTRACT

Aqueous polymer dispersions comprising a) 50-70% by weight of polymer particles composed of at least two different (co)polymers having glass transition temperatures each above 50° C. and synthesized from at least 80% by weight of at least one principal monomer, 0.1-10% by weight of at least one auxiliary monomer, and 0-3% by weight of at least one crosslinker molecule, 
 
the difference in the glass transition temperatures (T g ) of the different polymers being at least 10° C., and 
b) 30-50% by weight of at least one polyfunctional (meth)acrylate, the dispersion a) being subjected to physical and/or chemical deodorization.

The present invention relates to the preparation and use of aqueous,radiation-curable polymer dispersions for coating substrates.

In radiation curing the use of aqueous polymer dispersions is on theincrease with the aim of avoiding the need to handle monomers. Systemsof this kind are outstandingly suitable for open-pored substrates,especially paper and wood. Use is made predominantly of aqueousemulsions of unsaturated polyesters or polyester (meth)acrylates. Adisadvantage of these systems, however, is their liquid nature, oftenresulting in films which are tacky after the water has evaporated. Thiscauses problems especially in radiation curing of three-dimensionalarticles, since no curing takes place in the shadow regions and so tackyareas remain. For this reason, polyurethane dispersions with UV-curablegroups were developed. These dispersions are tack-free after filming.These dispersions are exclusively secondary dispersions, which aresituated very high in terms of their structure. Where inexpensivearomatic isocyanates such as TDI are used, the films produced from thedispersions have a high propensity toward yellowing, which rules outapplications involving white pigmentation.

Besides freedom from tack, the freedom of such coating systems fromsolvents and auxiliary film formers is desirable from an environmentalstandpoint. Moreover, a multiplicity of applications call for hardsurfaces on the coatings.

EP 486 278 discloses radiation-curable aqueous dispersions composed ofmixtures of an emulsion polymer (Tg<28° C.) that cannot be cured byradiation with a (meth)acrylate that can.

EP 624 610 describes comparable systems, but where the emulsion polymerabsolutely must have a Tg>30° C.

EP 232 016 describes emulsion polymers for which preliminarycrosslinking is mandatory (gel fraction>1%). The polymers are formulatedfor radiation curability by blending with a polyunsaturated compound orelse by copolymerization with crosslinkers of differing reactivity.

EP 736 573 describes multistage emulsion polymers which are formulatedfor radiation curability by blending with a polyunsaturated(meth)acrylate.

These prior art dispersions do not make it possible, however, to meetsatisfactorily the requirements set out above.

It is an object of the present invention to provide storage-stable,aqueous, radiation-curable polymer dispersions which can be formulatedsolventlessly and lead to tack-free coatings before radiation curing andto coatings of high hardness after radiation curing.

We have found that this object is achieved by aqueous polymerdispersions comprising

-   a) 50-70% by weight of polymer particles composed of at least two    different (co)polymers having glass transition temperatures each    above 50° C. and synthesized from    -   at least 80% by weight of at least one principal monomer,    -   0.1-10% by weight of at least one auxiliary monomer, and    -   0-3% by weight of at least one crosslinker molecule,        the difference in the glass transition temperatures (T_(g)) of        the different polymers being at least 10° C., and-   b) 30-50% by weight of at least one polyfunctional (meth)acrylate,    the dispersion a) being subjected to physical and/or chemical    deodorization.

The polymer dispersions of the invention contain 50-70% by weight ofpolymer particles and 30-50% by weight of polyfunctional (meth)acrylateb), such that the sum thereof makes 100% by weight.

Naturally, the polymer dispersions of the invention also contain water,in which the polymer particles are dispersed.

The aqueous polymer dispersions preferably contain 55-65% by weight ofa) and 35-45% by weight of b) and with particular preference 60-65% byweight of a) and 35-40% by weight of b).

The coatings obtained from the dispersion are tack-free before UV curingand have a high surface hardness after radiation curing.

The dispersions of the invention are stable on storage; that is whenstored at 50° C. for 14 days or at room temperature for six months nochange can be found. The dispersions of the invention can be filmed atbelow 20° C. even without auxiliary film formers, the coatingsobtainable with the dispersions being tack-free prior to UV curing andof high surface hardness and chemical resistance after radiation curing.

The (co)polymers which form the polymer particles in a) are composed ineach case of at least 80% by weight of at least one principal monomer,from 0.1 to 10% by weight of at least one auxiliary monomer, and from 0to 3% by weight of at least one crosslinker molelcule, with the provisothat the sum makes 100% by weight.

Principal monomers therein include, for example, methyl (meth)acrylate,ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate,iso-butyl (meth)acrylate, sec-butyl (meth)acrylate, n-pentyl(meth)acrylate, iso-pentyl (meth)acrylate, 2-methylbutyl (meth)acrylate,amyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylbutyl(meth)acrylate, pentyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, n-decyl (meth)acrylate,undecyl (meth)acrylate, n-dodecyl (meth)acrylate, 2-methoxyethyl(meth)acrylate, 2-ethoxyethyl (meth)acrylate, 4-methoxybutyl(meth)acrylate, 2-(2′-methoxyethoxy)ethyl (meth)acrylate, vinylchloride, vinylidene chloride, vinyl acetate, vinyl propionate, vinylbutyrate, methyl vinyl ketone, vinyltoluene, vinylnaphthalene, methylvinyl ether, ethyl vinyl ether, n-propyl vinyl ether, iso-propyl vinylether, n-butyl vinyl ether, sec-butyl vinyl ether, iso-butyl vinylether, tert-butyl vinyl ether, n-octyl vinyl ether, ethylene, propylene,1-butene, 2-butene, iso-butene, cyclopentene, cyclohexene,cyclododecene, butadiene, isoprene, chloroprene, styrene,α-methylstyrene, tert-butylstyrene, and mixtures thereof.

Preferred principal monomers are methyl methacrylate, n-butyl acrylate,ethylhexyl acrylate, and the aforementioned vinylaromatics; particularpreference is given to methyl methacrylate, n-butyl acrylate, andethylhexyl acrylate.

Auxiliary monomers are, for example, functionalized monomers, such asthose which carry carboxyl, hydroxyl, epoxy, allyl, carboxamide, amine,isocyanato, hydroxymethyl, methoxymethyl or silyloxy groups. Thesemonomers may be, for example, (meth)acrylic acid, (meth)acrylic acidformal, hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate,4-hydroxybutyl (meth)acrylate, 4-hydroxybutyl vinyl ether,benzophenoneglycidyl (meth)acrylate, 2-sulfoethyl (meth)acrylate,(meth)acrylamide, N-methylol(meth)acrylamide, fumaric acid, iso-propylfumarate, n-hexyl fumarate, fumaric monoamide, fumaric diamide, fumaricmononitrile, fumaric dinitrile, crotonic acid, glycidyl crotonate,itaconic acid, itaconic monoesters, itaconic anhydride, citraconic acid,citraconic monoesters, citraconic anhydride, succinic acid, maleic acid,monomethyl maleate, monoethyl maleate, monobutyl maleate, maleicanhydride, maleic monoamide, maleic diamide, N-methylolmaleamide,vinylsuccinimide, vinylimidazole, 2-vinylpyridine, 4-vinylpyridine,N-vinylpyrrolidone, N-vinylpiperidone, N-vinylcaprolactam, sodiumvinylsulfonate, tetraallyloxyethane, diallyl phthalate, diallylsuccinate, tetraallylethane, Tetraallyloxysilane, allyl glycidyl ether,ureido(meth)acrylate, triallyl cyanurate, triallyl isocyanurate,diketene, monoethylenically unsaturated carboxylic acids having 3 to 8carbon atoms and their water-soluble alkali metal, alkaline earth metalor ammonium salts such as, for example: acrylic acid, methacrylic acid,dimethylacrylic acid, ethacrylic acid, maleic acid, citraconic acid,methylenemalonic acid, crotonic acid, fumaric acid, mesaconic acid,itaconic acid, allylacetic acid, vinylacetic acid, and mixtures thereof.

Preferred auxiliary monomers are methacrylic acid, acrylic acid,acrylamide, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, and 4-hydroxybutyl vinyl ether; particular preference isgiven to acrylic acid, methacrylic acid, acrylamide, and hydroxyethylacrylate.

Crosslinker molecules are those polymerizable compounds having more thanone polymerizable double bond, such as vinyl ether groups or(meth)acrylate groups. Examples that may be mentioned include1,4-butanediol diacrylate, allyl methacrylate, ethylene glycol(meth)acrylate, propylene glycol (meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,2-neopentylglycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate,trimethylolpropane tri(meth)acrylate, trimethylolethanetri(meth)acrylate, pentaerythritol tri(meth)acrylate andtetra(meth)acrylate and divinylbenzene.

The at least two different (co)polymers of which the polymer particlesare composed are selected such that the polymers have glass transitiontemperatures which are above 50° C. and differ by at least 10° C.

The glass transition temperature can be determined by customary methodssuch as differential thermal analysis or differential scanningcalorimetry (DSC, preferably by the method of ASTM 3418/82, midpointtemperature).

The (co)polymerization may be conducted in a manner known per se to theskilled worker: for example, as a bulk, emulsion, miniemulsion,suspension, solution, precipitation, water-in-oil emulsion, invertedsuspension or microsuspension polymerization. Preference is given toprecipitation, suspension, solution, and emulsion polymerization,especially to emulsion polymerization.

The polymerization may take place free-radically, anionically,cationically or coordinatively, preferably free-radically.

One frequent—albeit not the only—method of preparing the (co)polymersreferred to is that of free-radical (co)polymerization in a solvent ordiluent.

The free-radical (co)polymerization in such monomers is effected, forexample, in aqueous medium in the presence of polymerization initiatorswhich break down into free radicals under polymerization conditions. The(co)polymerization may be performed within a wide temperature range,where appropriate under subatmospheric or superatmospheric pressure,generally at temperatures up to 100° C. The pH of the reaction mixtureis commonly set in the range from 4 to 10.

The monomer or monomer mixture is (co)polymerized using free-radicalpolymerization initiators, examples being radically decomposing azocompounds, such as 2,2′-azobisisobutyronitrile,2,2′-azobis-(2-amidinopropane) hydrochloride, and4,4′-azobis(4′-cyanopentanoic acid).

These compounds are generally used in the form of aqueous solutions, thelower concentration being governed by the amount of water that isacceptable in the (co)polymerization and the upper concentration by thesolubility of the respective compound in the solvent. The concentrationis generally from 0.1 to 30% by weight, preferably from 0.5 to 20% byweight, with particular preference from 1.0 to 10% by weight, based onthe solution.

The amount of initiators is generally from 0.1 to 10% by weight,preferably from 0.1 to 5% by weight, based on the monomers to be(co)polymerized. It is also possible for two or more differentinitiators to be used for the (co)polymerization.

Examples of solvents or diluents which can be used include water,alcohols, such as methanol, ethanol, n- or iso-propanol, n- oriso-butanol, or ketones, such as acetone, ethyl methyl ketone, diethylketone or iso-butyl methyl ketone.

Where appropriate the (co)polymerization may be conducted in thepresence of polymerization regulators, such as hydroxylammonium salts,chlorinated hydrocarbons, and thio compounds, such as tert-butylmercaptan, ethylacrylic thioglycolate, mercaptoethynol,mercaptopropyltrimethoxysilane, dodecyl mercaptan, and tert-dodecylmercaptan, for example, or alkali metal hypophosphites. In the(co)polymerization these regulators can be used, for example, in amountsof from 0 to 0.8 part by weight per 100 parts by weight of monomers tobe (co)polymerized, and reduce the molar mass of the resultant(co)polymer.

The preparation may also be effected, for example, by solutionpolymerization with subsequent dispersion in water.

Where the polymerization is conducted as an emulsion or suspensionpolymerization, use is made of ionic and/or nonionic emulsifiers and/orprotective colloids and/or stabilizers as surface-active compounds.

Depending on the conditions under which the (co)polymerization isconducted it produces (co)polymers or, where appropriate, crosslinkedparticles of differing molecular weights. (Co)polymers of high molecularweight are preferably prepared by (co)polymerizing the monomers inwater. (Co)polymers with high molecular weights are also obtained, forexample, by (co)polymerizing the monomers in the form of an invertedsuspension polymerization or by (co)polymerizing the monomers by themethod of water-in-oil polymerization.

In the case of the process of inverted suspension polymerization andalso of water-in-oil polymerization, the oil phase used comprisessaturated hydrocarbons, examples being hexane, heptane, cyclohexane, anddecalin, or aromatic hydrocarbons, such as benzene, toluene, xylene, andcumene. The ratio of oil phase to aqueous phase in the case of invertedsuspension polymerization is, for example, from 10:1 to 1:10.

(Co)polymer of low molecular weight is obtained if the(co)polymerization is conducted in the presence of polymerizationregulators or in a solvent which regulates the (co)polymerization,examples being alcohols, such as methanol, ethanol, n- or iso-propanol,or ketones, such as acetone, ethyl methyl ketone, diethyl ketone oriso-butyl methyl ketone.

(Co)polymers with low molecular weights are also obtained by means ofthe standard methods, i.e., using fairly large amounts of polymerizationinitiator or using polymerization regulators, or through combinations ofsaid measures.

Preferred (co)polymers are those having an average molecular weightM_(w) of more than 20000, with particular preference more than 50000(M_(w) is determined by gel permeation chromatography with polystyreneas standard and tetrahydrofuran as eluent).

In the emulsion polymerization use is made of ionic and/or nonionicemulsifiers and/or protective colloids and/or stabilizers assurface-active compounds.

A detailed description of suitable protective colloids can be found inHouben-Weyl, Methoden der organischen Chemie, Volume XIV/1,Makromolekulare Stoffe [Macromolecular Substances], Georg-Thieme-Verlag,Stuttgart, 1961, pp. 411 to 420. Suitable emulsifiers include anionic,cationic, and nonionic emulsifiers. As accompanying surface-activesubstances it is preferred to use exclusively emulsifiers, whosemolecular weights, unlike those of protective colloids, are normallybelow 2000 g/mol. Where mixtures of surface-active substances are used,the individual components must of course be compatible with one another,something which can be checked in case of doubt by means of a fewpreliminary tests. It is preferred to use anionic and nonionicemulsifiers as surface-active substances. Common accompanyingemulsifiers are, for example, ethoxylated fatty alcohols (EO units: 3 to50, alkyl: C₈ to C₁₈), ethoxylated mono-, di-, and trialkylphenols (EOunits: 3 to 50, alkyl: C₄ to C₉), alkali metal salts of dialkyl estersof sulfosuccinic acid and also alkali metal and ammonium salts of alkylsulfates (alkyl: C₈ to C₁₈), of ethoxylated alkanols (EO units: 4 to 30,alkyl: C₁₂ to C₁₈), of ethoxylated alkylphenols (EO units: 3 to 50,alkyl: C₄ to C₉), of alkylsulfonic acids (alkyl: C₁₂ to C₁₈), and ofalkylarylsulfonic acids (alkyl: C₉ to C₁₈).

Sulfonates, sulfates, and carboxylates are preferred, with appropriatemetal counterions.

Suitable emulsifiers can also be found in Houben-Weyl, Methoden derorganischen Chemie, Volume 14/1, Makromolekulare Stoffe, Georg ThiemeVerlag, Stuttgart, 1961, pages 192 to 208.

Trade names of emulsifieres are, for example, Dowfax®2 A1, Emulan® NP50, Dextrol® OC 50, Emulgator 825, Emulgator 825 S, Emulan® OG, Texapon®NSO, Nekanil® 904 S, Lumiten® I-RA, Lumiten E 3065, Disponil FES 77,Lutensol AT 18, Steinapol VSL, and Emulphor NPS 25.

The surface-active substance is usually used in amounts of from 0.1 to20% by weight, preferably from 1 to 20 and with particular preferencefrom 1.5 to 10% by weight based on the monomers to be polymerized.

Water-soluble initiators for the emulsion polymerization are, forexample, ammonium and alkali metal salts of peroxodisulfuric acid, e.g.,sodium peroxodisulfate, hydrogen peroxide, or organic peroxides, e.g.,tert-butyl hydroperoxide.

Particularly suitable initiator systems are those known asreduction-oxidation (redox) systems.

The redox initiator systems are composed of at least one, usuallyinorganic, reducing agent and one organic or inorganic oxidizing agent.

The oxidizing component comprises, for example, the emulsionpolymerization initiators already mentioned above.

The reducing components comprise, for example, alkali metal salts ofsulfurous acid, such as sodium sulfite, sodium hydrogen sulfite, alkalimetal salts of disulfurous acid such as sodium disulfite, bisulfiteaddition compounds with aliphatic aldehydes and ketones, such as acetonebisulfite, or reducing agents such as hydroxymethanesulfinic acid andits salts, or ascorbic acid. The redox initiator systems may be usedtogether with soluble metal compounds whose metallic component is ableto exist in a plurality of valence states.

Examples of customary redox initiator systems include ascorbicacid/iron(II) sulfate/sodium peroxodisulfate, tert-butylhydroperoxide/sodium disulfite, and tert-butyl hydroperoxide/Nahydroxymethanesulfinate. The individual components, the reducingcomponent for example, may also be mixtures, an example being a mixtureof the sodium salt of hydroxymethanesulfinic acid with sodium disulfite.

These compounds are generally used in the form of aqueous solutions oremulsions, the lower concentration being governed by the amount of waterthat is acceptable in the dispersion and the upper concentration by thesolubility of the respective compound in water. The concentration isgenerally from 0.1 to 30% by weight, preferably from 0.5 to 20% byweight, with particular preference from 1.0 to 10% by weight, based onthe solution.

The amount of the initiators is generally from 0.1 to 10% by weight,preferably from 0.5 to 5% by weight, based on the monomers to bepolymerized. It is also possible for two or more different initiators tobe used in the emulsion polymerization.

During the polymerization it is possible to use regulators, in amountsfor example of from 0 to 0.8 part by weight per 100 parts by weight ofthe monomers to be polymerized; their effect is to reduce the molarmass. Suitable, for example, are compounds containing a thiol group,such as tert-butyl mercaptan, ethylacrylic thioglycolate,mercaptoethynol, mercaptopropyltrimethoxysilane, and tert-dodecylmercaptan.

The emulsion polymerization takes place generally at from 30 to 130° C.,preferably at from 50 to 95° C. The polymerization medium may consisteither of water alone or of mixtures of water with water-miscibleliquids such as methanol. Preferably, just water is used. The emulsionpolymerization may be conducted either as a batch operation or in theform of a feed process, including staged or gradient procedures.Preference is given to the feed process, in which a portion of thepolymerization batch is introduced as an initial charge and is heated tothe polymerization temperature, polymerization is begun, and then theremainder of the polymerization batch is supplied to the polymerizationzone continuously, in stages or under a concentration gradient, usuallyby way of two or more spatially separate feed streams, of which one ormore contain the monomers in neat or emulsified form, and during thisaddition the polymerization is maintained. In order to obtain thedesired particle size more effectively, for example, it is possible toinclude a polymer seed in the initial polymerization charge, at 0.1-3%by weight, for example.

The manner in which the initiator is added to the polymerization vesselin the course of free-radical aqueous emulsion polymerization is knownto the skilled worker. It may either be included in its entirety in theinitial charge to the polymerization vessel or else introducedcontinuously or in stages in the course of the free-radical aqueousemulsion polymerization, at the rate at which it is consumed.Specifically this will depend both on the chemical nature of theinitiator system and on the polymerization temperature. Preferably, someis included in the initial charge and the remainder is supplied to thepolymerization zone at the rate of consumption.

In order to remove the residual monomers it is common to add initiatorafter the end of the emulsion polymerization proper as well, i.e., aftera monomer conversion of at least 95%.

In the case of the feed process, the individual components can be addedto the reactor from the top, at the side or from below, through thereactor floor.

In the case of emulsion polymerization, aqueous polymer dispersions withsolids contents of generally from 15 to 75% by weight, preferably from40 to 75% by weight, are obtained.

For a high space/time yield of the reactor, dispersions with a very highsolids content are preferred. In order to be able to achieve solidscontents >60% by weight, a bimodal or polymodal particle size ought tobe set, since otherwise the viscosity becomes too high and thedispersion unmanageable. Creating a new generation of particles can bedone, for example, by adding seed (EP 81083), by adding excessquantities of emulsifier, or by adding miniemulsions. A furtheradvantage associated with the combination of low viscosity and highsolids content is the improved coating behavior. Creating one or morenew generations of particles can be done at any point in time. Itdepends on the particle size distribution which is being aimed at for alow viscosity.

The copolymer is preferably used in the form of its aqueous dispersion.

Where the polymerization is effected in the presence of a seed latex,such a seed is not counted in the number of polymers which form thepolymer particle.

The polymer particles preferably have average sizes of 100-500 nm, withparticular preference 100-250 nm, in a distribution which with veryparticular preference is monomodal.

The particles may be homogeneous or heterogeneous in construction. Inthe case of a heterogeneous construction, it is possible for there to beone core and one or more shells.

Where the particles are composed of core and at least one shell, thenthe refractive indices of core and shell(s) should be as close aspossible, for enhanced transparency. The difference is preferably notmore than 0.1, with particular preference not more than 0.075, and withvery particular preference not more than 0.05.

The polymer dispersions of the invention are obtainable by chemicallyand/or physically deodorizing (aftertreating) the dispersions a) andthen incorporating the polyfunctional (meth)acrylate b). The inventionlikewise provides a process for preparing polymer dispersions of theinvention by deodorizing the dispersions a) chemically and/or physicallyand then incorporating b).

With the aim of reducing the amount of residual monomers, thepolymerization reaction is followed by chemical and/or physical,preferably chemical, deodorization of the dispersion a).

A physical deodorization may consist in stripping the dispersion withsteam, an oxygenous gas, preferably air, nitrogen or supercriticalcarbon dioxide in, for example, a stirred vessel, as described in DE-B12 48 943, or in a countercurrent column, as described in DE-A 196 21027.

Depending on the amounts and on the boiling points of the components tobe separated off, deodorization takes place in one or more stages.Generally speaking, the volatile constituents with a boiling point atatmospheric pressure of up to about 200° C. are largely separated off.

This can be combined with a chemical deodorization, that is, apostpolymerization performed by adding an initiator, as described, forexample, in DE-A 198 28 183.

As oxidizing and reducing agent components it is possible, for example,to use organic or inorganic hydroperoxides, such as tert-butylhydroperoxide, butyl peroxide, hydrogen peroxide, alkali metal oralkaline earth metal persulfates, perborates or percarbonates, and alsosodium hydroxymethylsulfinate, ascorbic acid, Mohr's salt, etc.,preferably tert-butyl hydroperoxide and sodium hydroxymethylsulfinate.

The chemical deodorization is generally carried out at a temperature offrom 40 to 90° C. through a period ranging from 15 minutes to 3 hours.

In this procedure, either both redox components can be metered in,simultaneously or in portions, or some or all of one component can beincluded in the initial charge and the remainder of the component and/orother component can be metered in over a period ranging, for example,from 5 to 120 minutes, preferably from 30 to 90 minutes, and withparticular preference from 45 to 75 minutes. Metering may be carried outcontinuously or else discontinuously.

The amount of reducing and/or oxidizing component used is in each case0.01-0.5% by weight, preferably 0.05-0.2% by weight, based on the amountof polymer in the dispersion to be deodorized. The ratio of the amountof reducing component used to the amount of oxidizing component used isarbitrary.

Chemical deodorization may be followed by neutralization of thedispersion using, for example, sodium hydroxide, potassium hydroxide,sodium hydrogen carbonate, potassium hydrogen carbonate, sodiumcarbonate, potassium carbonate or milk of lime to the desired pH of, forexample, from 6 to 8, preferably from 6.5 to 7.5.

For the further removal of, say, residual oxidizing constituents,further reducing agent can be added, and may be the same one ordifferent one than that mentioned above, and is added in amounts of0.01-0.5% by weight, preferably 0.01-0.2% by weight, based on the amountof polymer in the dispersion to be deodorized, so that the reducingagent is used as the whole amount in excess over the oxidizing agent.This further reducing agent may be selected from the followingcomponents: sodium hydroxymethylsulfinate, ascorbic acid, Mohr's salt,etc. Ascorbic acid is used with preference.

Following deodorization, the residual monomer content is generally notmore than 300 ppm.

It has surprisingly been found that by virtue of chemical deodorizationit was possible to achieve an increased storage stability of thedispersion blended with polyfunctional (meth)acrylate b) (see below).

Polyfunctional (meth)acrylates b) are compounds which carry at least 2,preferably 3-10, with particular preference 3-6, with very particularpreference 3-4, and in particular 3 (meth)acrylate groups, preferablyacrylate groups.

These may be, for example, esters of (meth)acrylic acid withpolyalcohols which appropriately have a functionality of at least two.

Examples of such polyalcohols are at least dihydric polyols,polyetherols or polyesterols or polyacrylate polyols having an averageOH functionality of at least 2, preferably from 3 to 10.

Examples of polyalcohols with a functionality of at least two are1,2-propanediol, ethylene glycol, 2,2-dimethyl-1,2-ethanediol,1,3-propanediol, 1,2-butanediol, 1,4-butanediol,3-methylpentane-1,5-diol, 2-ethylhexane-1,3-diol,2,4-diethyloctane-1,3-diol, 1,6-hexanediol, polyTHF with a molar mass ofbetween 162 and 378, poly-1,3-propanediol with a molar mass between 134and 598, poly-1,2-propanediol with a molar mass between 134 and 598,polyethylene glycol with a molar mass between 106 and 458, neopentylglycol, neopentyl glycol hydroxypivalate, 2-ethyl-1,3-propanediol,2-methyl-1,3-propanediol, 2-ethyl-1,3-hexanediol,2,2-bis(4-hydroxycyclohexyl)propane, 1,1-, 1,2-, 1,3- and1,4-cyclohexanedimethanol, 1,2-, 1,3- and 1,4-cyclohexanediol,trimethylolbutane, trimethylolpropane, trimethylolethane,pentaerythritol, glycerol, ditrimethylolpropane, dipentaerythritol,sorbitol, mannitol, diglycerol, threitol, erythritol, adonitol(ribitol), arabitol (lyxitol), xylitol, dulcitol (galactitol), maltitolor isomalt.

Further suitable polyalcohols with a functionality of at least two arealkoxylated polyalcohols.

Examples of suitable alkylene oxides include ethylene oxide, propyleneoxide, iso-butylene oxide, vinyloxirane, and styrene oxide.

The alkylene oxide chain may be composed preferably of ethylene oxide,propylene oxide and/or butylene oxide units. Such a chain may becomposed of one species of an alkylene oxide or of a mixture of alkyleneoxides. Where a mixture is used the different alkylene oxide units maybe present randomly or as a block or as blocks of individual species. Apreferred alkylene oxide is ethylene oxide, propylene oxide or a mixturethereof, with particular preference ethylene oxide or propylene oxide,and with very particular preference ethylene oxide.

The number of alkylene oxide units in the chain is, for example, from 1to 20, preferably from 1 to 10, with particular preference 1-5, andespecially 1-3, and very preferably 1, based on the respective hydroxylgroups of the polyalcohol.

Suitable starter alcohols include the abovementioned polyalcohols with afunctionality of at least two.

Examples of suitable polyesterols are those preparable by esterifyingpolycarboxylic acids, preferably dicarboxylic acids, with diols and atleast one of the abovementioned polyalcohols.

The starting materials for such polyesterols are known to the skilledworker. As polycarboxylic acids it is possible with preference to useoxalic acid, maleic acid, fumaric acid, succinic acid, glutaric acid,adipic acid, sebacic acid, dodecanedioic acid, o-phthalic acid,isophthalic acid, terephthalic acid, trimellitic acid, azelaic acid,1,4-cyclohexanedicarboxylic acid or tetrahydrophthalic acid, theirisomers and hydrogenation products, and also esterifiable derivatives,such as anhydrides or dialkyl esters, examples being C₁-C₄ alkyl esters,preferably methyl, ethyl or n-butyl esters of said acids.

Suitable hydroxyl-carrying carboxylic acids or lactones include4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, pivalolactone, andε-caprolactone.

Suitable diols include polyTHF with a molar mass of between 162 and 738,poly-1,2- or -1,3-propanediol with a molar mass of between 134 and 598,polyethylene glycol with a molar mass of between 106 and 458,3-methylpentane-1,5-diol, 2-ethylhexane-1,3-diol,2,4-diethyloctane-1,3-diol, 1,6-hexanediol, 1,4-butanediol, neopentylglycol hydroxypivalate, 2-ethyl-1,3-propanediol,2-methyl-1,3-propanediol, 2-ethyl-1,3-hexanediol,2,2-bis(4-hydroxycyclohexyl)propane, 1,1-, 1,2-, 1,3- and1,4-cyclohexanedimethanol, and 1,2-, 1,3- and 1,4-cyclohexanediol.

Suitable polyalcohols include the abovementioned alcohols offunctionality at least two, preferably neopentyl glycol,trimethylolpropane, trimethylolethane or pentaerythritol.

The molecular weights M_(n) of the polyesterols and polyetherols arepreferably between 100 and 4000 (M_(n) is determined by gel permeationchromatography using polystyrene as standard and tetrahydrofuran aseluent).

Further possible polyfunctional (meth)acrylates b) are polyester(meth)acrylates, epoxy (meth)acrylates, urethane (meth)acrylates, and(meth)acrylated polyacrylates. Instead of the (meth)acrylate groups itis also possible to use other groups which can be polymerizedfree-radically or cationically.

Urethane (meth)acrylates, for example, are obtainable by reactingpolyisocyanates with hydroxyalkyl (meth)acrylates or hydroxyalkyl vinylethers and, where appropriate, chain extenders such as diols, polyols,diamines, polyamines or dithiols or polythiols. Urethane (meth)acrylateswhich can be dispersed in water without the addition of emulsifiersadditionally contain ionic and/or nonionic hydrophilic groups, which areintroduced into the urethane, for example, by synthesis components suchas hydroxycarboxylic acids.

Preferred polyfunctional (meth)acrylates b) are trimethylolpropanetriacrylate, acrylates of ethoxylated and/or propoxylatedtrimethylolpropane, pentaerythritol, glycerol or ditrimethylolpropane.Particularly preferred acrylates are those of ethoxylated and/orpropoxylated trimethylolpropane or pentaerythritol.

In one preferred embodiment the at least one polyfunctional(meth)acrylate b) is incorporated into the dispersion containing thepolymer particles at elevated temperature, i.e., at above roomtemperature, preferably above 40° C., with particular preference at atemperature from 60 to 100° C., and with very particular preference atfrom 80 to 90° C.

The amount of polyfunctional (meth)acrylates b) is chosen so that theresulting blend has a minimum film formation temperature of less than20° C.

The solids content of the dispersions can be adjusted in accordance withthe desired viscosity, from 50 to 500 mPas for example, and is generallysituated between 20 and 80% by weight, in particular between 30 and 70%by weight.

The dispersions of the invention may further comprise additives knownper se to the skilled worker, examples being photoinitiators and otheradditives.

As photoinitiators it is possible to use photoinitiators which are knownto the skilled worker, examples being those in “Advances in PolymerScience”, Volume 14, Springer Berlin 1974 or in K. K. Dietliker,Chemistry and Technology of UV and EB Formulation for Coatings, Inks andPaints, Volume 3; Photoinitiators for Free Radical and CationicPolymerization, P. K T. Oldring (Eds), SITA Technology Ltd, London.

Suitable examples include monoacyl- and bisacylphosphine oxides, asdescribed, for example, in EP-A 7 508, EP-A 57 474, DE-A 196 18 720,EP-A 495 751 or EP-A 615 980, such as2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin® TPO), ethyl2,4,6-trimethylbenzoylphenylphosphinate, Irgacure® 819 from CibaSpezialitätenchemie (bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide),benzophenones, hydroxyacetophenones, phenylglyoxylic and its derivativesor mixtures of these photoinitiators. Examples that may be mentionedinclude benzophenone, acetophenone, acetonaphthoquinone, methyl ethylketone, valerophenone, hexanophenone, α-phenylbutyrophenone,p-morpholinopropiophenone, dibenzosuberone, 4-morpholinobenzophenone,4-morpholinodeoxybenzoin, p-diacetylbenzene, 4-aminobenzophenone,4′-methoxyacetophenone, β-methylanthraquinone, tert-butylanthraquinone,anthraquinonecarboxylic esters, benzaldehyde, α-tetralone,9-acetylphenanthrene, 2-acetylphenanthrene, 10-thioxanthenone,3-acetylphenanthrene, 3-acetylindole, 9-fluorenone, 1-indanone,1,3,4-triacetylbenzene, thioxanthen-9-one, xanthen-9-one,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone,2,4-di-iso-propylthioxanthone, 2,4-dichlorothioxanthone, benzoin,benzoin iso-butyl ether, chloroxanthenone, benzoin tetrahydropyranylether, benzoin methyl ether, benzoin ethyl ether, benzoin butyl ether,benzoin iso-propyl ether, 7H-benzoin methyl ether,benz[de]anthracen-7-one, 1-naphthaldehyde,4,4′-bis(dimethylamino)benzophenone, 4-phenylbenzophenone,4-chlorobenzophenone, Michler's ketone, 1-acetonaphthone,2-acetonaphthone, 1-benzoylcyclohexan-1-ol,2-hydroxy-2,2-dimethylacetophenone, 2,2-dimethoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone,1-hydroxyacetophenone, acetophenone dimethyl ketal,o-methoxybenzophenone, triphenylphosphine, tri-o-tolylphosphine,benz[a]anthracene-7,12-dione, 2,2-diethoxyacetophenone, benzil ketals,such as benzil dimethyl ketal,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butylanthraquinone, 1-chloroanthraquinone, and2-amylanthraquinone, and 2,3-butanedione.

Also suitable are nonyellowing or low-yellowing photoinitiators of thephenylglyoxylic ester type, as described in DE-A 198 26 712, DE-A 199 13353 or WO 98/33761.

Preferred among these are the recited acylphosphine oxides,benzophenones, hydroxyacetophenones, and phenylglyoxylic acids.

In particular it is also possible to use mixtures of differentphotoinitiators.

It is also possible to use incorporable photoinitiators. Incorporablephotoinitiators carry polymerizable groups attached to thephotoinitiator parent structure by way of spacer groups. Suchincorporable photoinitiators are described, for example, in DE-A 195 24812, EP-A 281 941, and WO 00/24527. Preferred among these are4-acryloyloxy-2′-chlorobenzophenone,4-acryloyloxy-3′-chlorobenzophenone,4-acryloyloxy-4′-chlorobenzophenone,4-(6′-acryloyloxy-2′-oxa-1′-oxohexyloxy)benzophenone or1,1-dimethyl-1-hydroxy-4′-(2″-acryloyloxyethoxy)acetophenone.

The photoinitiators may be used alone or in combination with aphotopolymerization promoter, of the benzoic acid or amine type, forexample, or of similar type.

Preference is given to photoinitiators containing an acylphosphine oxideunit or a benzophenone unit.

The photoinitiators are generally added in amounts of from 0.2 to 10% byweight.

Examples of additives that can be used include antioxidants, oxidationinhibitors, stabilizers, activators (accelerators), fillers, pigments,dyes, degassing agents, luster agents, antistats, flame retardants,thickeners, thixotropic agents, leveling assistants, binders, antifoams,fragrances, surface-active agents, viscosity modifiers, plasticizers,plastifiers, tackifying resins (tackifiers), chelating agents,delusterants, defoamers or compatibilizers.

It is also possible as a component to have one or more photochemicallyand/or thermally activatable initiators, examples being potassiumperoxodisulfate, dibenzoyl peroxide, cyclohexanone peroxide,di-tert-butyl peroxide, azobis-iso-butyronitrile, cyclohexylsulfonylacetyl peroxide, di-iso-propyl percarbonate, tert-butyl peroctoate orbenzpinacol, and also, for example, those thermally activatableinitiators which have a half life at 80° C. of more than 100 hours, suchas di-t-butyl peroxide, cumene hydroperoxide, dicumyl peroxide, t-butylperbenzoate, silylated pinacols, which are available commercially, forexample, under the trade name ADDID 600 from Wacker, orhydroxyl-containing amine N-oxides, such as2,2,6,6-tetramethylpiperidine-N-oxyl,4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, etc.

Further examples of suitable initiators are described in “PolymerHandbook”, 2^(nd) edition, Wiley & Sons, New York.

Suitable thickeners include, in addition to free-radically(co)polymerized (co)polymers, customary organic and inorganic thickenerssuch as hydroxymethylcellulose or bentonite.

As chelating agents it is possible, for example, to useethylenediamineacetic acid and its salts and also β-diketones.

Suitable fillers include silicates, examples being silicates obtainableby hydrolysis of silicon tetrachloride, such as Aerosil® from Degussa,siliceous earth, talc, clay, mica, aluminum silicates, magnesiumsilicates, calcium carbonates, calcium and barium sulfates, aluminumhydroxides and aluminum oxides, etc., and organic fillers, such aspolyacrylic acids, with a molar weight, for example, of between 2000 and300000, and also cellulose.

Suitable stabilizers include typical UV absorbers such as oxanilides,triazines, and benzotriazole (the latter obtainable as Tinuvin® gradesfrom Ciba-Spezialitätenchemie), and benzophenones. They can be usedalone or together with suitable free-radical scavengers, examples beingsterically hindered amines such as 2,2,6,6-tetramethylpiperidine,2,6-di-tert-butylpiperidine or derivatives thereof, e.g.,bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate. Stabilizers are commonlyused in amounts of from 0.1 to 5.0% by weight, based on the solidcomponents present in the formulation.

Stabilizers which are additionally suitable are, for example, N-oxyls,such as 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl,4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl,4-acetoxy-2,2,6,6-tetramethylpiperidine-N-oxyl,2,2,6,6-tetramethylpiperidine-N-oxyl,4,4′,4″-tris(2,2,6,6-tetramethyl-piperidine-N-oxyl) phosphite or3-oxo-2,2,5,5-tetramethyl-pyrrolidine-N-oxyl, phenols and naphthols,such as p-aminophenol, p-nitrosophenol, 2-tert-butylphenol,4-tert-butylphenol, 2,4-di-tert-butylphenol,2-methyl-4-tert-butylphenol, 4-methyl-2,6-tert-butylphenol(2,6-tert-butyl-p-cresol) or 4-tert-butyl-2,6-dimethylphenol, quinones,such as hydroquinone or hydroquinone monomethyl ether, for example,aromatic amines, such as N,N-diphenylamine, N-nitrosodiphenylamine,phenylenediamines, such as N,N′-dialkyl-para-phenylenediamine, the alkylradicals being identical or different, being composed in each caseindependently of one another of from 1 to 4 carbon atoms, and beingstraight-chain or branched, hydroxylamines, such asN,N-diethylhydroxylamine, urea derivatives, such as urea or thiourea,phosphorus compounds, such as triphenylphosphine, triphenyl phosphite ortriethyl phosphite, or sulfur compounds, such as diphenyl sulfide orphenothiazine, for example.

The dispersions of the invention are particularly suitable for coatingsubstrates such as paper, paperboard, cardboard, textile, leather,nonwovens, surfaces made of plastic, wood, glass, ceramic, mineralconstruction materials, such as shaped cement slabs and fiber cementslabs, or metals or coated metals, preferably glass, paper, plastics ormetals.

The dispersions of the invention are particularly suitable for coatingpaper and especially for producing abrasive paper.

The substrates are coated in accordance with standard techniques knownto the skilled worker, which involve applying at least one dispersion ofthe invention to the target substrate in the desired thickness andremoving the volatile constituents of the dispersions, with heatingwhere appropriate. This operation may be repeated one or more times ifdesired. Application to the substrate may take place in a known manner,for example, by spraying, troweling, knife coating, brushing, rollingon, roller coating or flow coating. The coating thickness is situatedgenerally within a range from about 3 to 1000 g/m² and preferably from10 to 200 g/m².

The invention further provides a method of coating substrates whereinthe dispersions of the invention, admixed where appropriate with furthertypical coatings additives and thermally curable resins, are applied tothe substrate and dried where appropriate, cured with electron beams orUV exposure under an oxygenous atmosphere or, preferably, under inertgas, and treated thermally, where appropriate at temperatures up to thelevel of the drying temperature, and subsequently at temperatures up to160° C., preferably between 60 and 160° C.

The method of coating substrates may also be implemented following theapplication of the dispersions of the invention by first thermallytreating at temperatures up to 160° C., preferably between 60 and 160°C., and then curing with electron beams or UV exposure under oxygen or,preferably, under inert gas.

If desired, the curing of the films formed on the substrate may takeplace exclusively by means of heat. In general, however, the coatingsare cured both by exposure to high-energy radiation and thermally.

If desired, if two or more layers of the coating composition are appliedone on top of another, it is possible for thermal and/or radiationcuring to take place after each coating operation. Examples of suitableradiation sources for the radiation curing include low, medium, and highpressure mercury lamps and also fluorescent tubes, pulsed lamps, metalhalide lamps, electronic flash devices, which allow radiation curingwithout a photoinitiator, or excimer emitters. Radiation curing takesplace through exposure to high-energy radiation, i.e., UV radiation ordaylight, preferably light in the wavelength range of λ=200 to 700 nm,with particular preference of λ=200 to 500 nm, and with very particularpreference of λ=250 to 400 nm, or by bombardment with high-energyelectrons (electron beams; 150 to 300 keV). Examples of radiationsources used include high pressure mercury vapor lamps, lasers, pulsedlamps (flash light), halogen lamps, and excimer emitters. The radiationdose normally sufficient for crosslinking in the case of UV curing issituated within a range from 80 to 3000 mJ/cm².

It is of course also possible to use two or more radiation sources forcuring, from two to four for example.

These sources may also each emit in different wavelength ranges.

Irradiation may be carried out where appropriate in the absence ofoxygen as well, under an inert gas atmosphere, for example. Suitableinert gases include preferably nitrogen, noble gases, carbon dioxide, orcombustion gases. Irradiation may also take place by covering thecoating material with transparent media. Examples of transparent mediaare polymer films, glass or liquids, such as water. Particularpreference is given to irradiation in the manner described in DE-A1 19957 900.

In addition to or instead of thermal curing, curing may also take placeby NIR radiation, which here refers to electromagnetic radiation in thewavelength range from 760 nm to 2.5 μm, preferably from 900 to 1500 nm.

Where appropriate, if two or more layers of the coating composition areapplied one on top of another, a thermal, NIR and/or radiation cure canbe carried out after each coating operation.

The invention further provides a method of coating substrates whichcomprises

-   i) coating a substrate with a dispersion as described above,-   ii) removing volatile constituents of the dispersion for the purpose    of film forming under conditions under which the photoinitiator    essentially does not yet form any free radicals,-   iii) where appropriate, exposing the film formed in step ii) to    high-energy radiation, the film being precured, and then, where    appropriate, machining the article coated with the precured film or    contacting the surface of the precured film with another substrate,    and-   iv) completing curing of the film thermally.

Steps iv) and iii) may also be carried out in reverse order: that is,the film can be cured first thermally and then with high-energyradiation.

For the production of abrasive papers, the abrasive is scattered ontothe coating while it is still wet, prior to drying, and only then isdrying carried out. The abrasive material comprises, for example,diamond, garnet, pumice, tripel, silicon carbide, emery, corundum,aluminum oxides, kieselguhr, sand (abrasuve sand), gypsum, boroncarbide, borides, carbides, nitrides, and cerium oxide. This is followedby radiation curing. The resultant coatings feature very good mechanicalproperties, particularly a high surface hardness.

ppm figures and percentages used in this text are by weight unlessotherwise specified.

EXAMPLES

A 2 l polymerization vessel with stirrer and reflux condenser wascharged with

-   445.0 g of deionized water and-   35.0 g of a 33% by weight aqueous polymer latex (prepared by    free-radically initiated emulsion polymerization of a monomer    mixture composed of 100% by weight styrene; polymer solids content    33% by weight) having a weight-average particle diameter of 27 nm,    and this initial charge was heated to 85° C. under nitrogen and with    stirring. Then 4.6 g of feed stream III were added. Thereafter,    beginning simultaneously, while maintaining stirring and the    reaction temperature, the remainder of feed stream III was added    continuously over the course of 180 minutes and feed strean I was    added continuously over the course of 90 minutes to the    polymerization batch. After the end of feed stream I, continuous    metered addition of feed stream III was continued for 60 minutes and    then feed stream II was metered in over the course of 30 minutes.    After the end of feed stream II, reaction was continued at reaction    temperature for 30 minutes. Subsequently, beginning simultaneously    two separate feed streams comprising 6.2 g of a 9.5% strength by    weight aqueous solution of tert-butyl hydroperoxide and,    respectively, 38.0 g of a 2% by weight aqueous solution of sodium    hydroxymethanesulfinate, were metered in continuously over the    course of 60 minutes. After the end of the feed streams, at 85° C.,    the pH of the dispersion was neutralized using 14.2 g of 25%    strength by weight sodium hydroxide solution and then 9.1 g of a    2.5% strength by weight aqueous solution of ascorbic acid were    metered in over 5 minutes. After the end of the addition, 344.5 g of    an ethoxylated trimethylolpropane triacrylate (average degree of    ethoxylation 1 per OH group; stabilized with 1 pphm (parts per    hundred monomers, i.e. based on 100 parts by weight of monomers) of    hydroquinone monomethyl ether and 0.1 pphm of    2,4-di-tert-butylphenol) were metered in with stirring over the    course of 40 minutes. The reaction mixture was then cooled to    20-25° C. (room temperature) and filtered through a Perlon filter    with a mesh size of 125 m.

Feed stream I is an emulsion prepared from:

-   357.3 g of deionized water-   10.0 g of a 20% strength by weight aqueous solution of a fatty    alcohol ethoxylate (alkyl radical: C₁₆-C₁₈; average degree of    ethoxylation: 18)-   12.8 g of a 45% strength by weight aqueous solution of Dowfax® 2A1-   5.7 g of methacrylic acid (MAA)-   5.7 g of butanediol diacrylate-   86.1 g of n-butyl acrylate (nBA)-   315.8 g of methyl methacrylate (MMA)

Feed stream II is an emulsion prepared from:

-   160.8 g of deionized water-   4.3 g of a 20% strength by weight aqueous solution of a fatty    alcohol ethoxylate (alkyl radical: C₁₆-C₁₈; average degree of    ethoxylation: 18)-   5.1 g of a 45% strength by weight aqueous solution of Dowfax® 2A1-   11.5 g of acrylic acid (AA)-   2.9 g butanediol diacrylate-   172.2 g of methyl methacrylate (MMA)

Feed stream III:

-   1.1 g of ammonium peroxodisulfate-   44.8 g of deionized water

The resulting aqueous dispersion had a solids content of 45.6% by weightand a pH of 7.4.

Comparative Example 1

The comparative example was prepared in the same way as example 1. Thecomposition of feed streams I and II is as follows:

Feed stream I is an emulsion prepared from:

-   357.3 g of deionized water-   10.0 g of a 20% strength by weight aqueous solution of a fatty    alcohol ethoxylate (alkyl radical: C₁₆-C₁₈; average degree of    ethoxylation: 18)-   12.8 g of a 45% strength by weight aqueous solution of Dowfax® 2A1-   5.7 g of methacrylic acid (MA)-   5.7 g of butanediol diacrylate-   302.4 g of n-butyl acrylate (nBA)-   97.5 g of methyl methacrylate (MMA)

Feed stream II is an emulsion prepared from:

-   160.8 g of deionized water-   4.3 g of a 20% strength by weight aqueous solution of a fatty    alcohol ethoxylate (alkyl radical: C₁₆-C₁₈; averge degree of    ethoxylation: 18)-   5.1 g of a 45% strength by weight aqueous solution of Dowfax® 2A1-   11.5 g of acrylic acid (AA)-   2.9 g of butanediol diacrylate-   134.8 g of methyl methacrylate (MMA)-   39.5 g of n-butyl acrylate (nBA)

The resulting aqueous dispersion had a solids content of 45.2% by weightand a pH of 7.4.

Analysis

The solids contents were determined by drying an aliquot in a dryingoven at 140° C. for 6 hours. Two separate measurements were carried outin each case. The figure quoted in the respective examples representsthe average of the two measurements.

The pH was determined using a glass electrode and a Handylab1 pH meterfrom Schott, calibrated to buffers with pH values of 4.0, 7.0, and 9.0.

2. Coating

Dispersions were blended with 1.3% by weight of Irgacure® 500. Thesubstrate was then coated using a doctor blade (200 μm, wet), dried at60° C. for 15 minutes and then cured with UV radiation.

Performance Properties: Example 1 Comparative example 1 Pendulum damping 7 10 before UV curing after UV curing 103 40 Storage stability at >14days not measured 50° C. Tackiness before curing + −

The pendulum damping was tested in accordance with DIN 53157.

For the storage stability test, 250 ml of the dispersion were stored ina closed vessel at 50° C. The criterion for storage stability was met ifno phase separation or changes in viscosity were observed after 14 days.

The tackiness of the uncured coatings was determined qualitatively:

-   tack-free=+-   almost tack-free=0-   tacky=−

1. An aqueous polymer dispersion comprising a) 50-70%, by weights of polymer particles composed of at least two different (co)polymers having glass transition temperatures, each above 50° C., and synthesized from at least 80%, by weights of at least one principal monomer, 0.1-10%, by weight, of at least one auxiliary monomer, and 0-3%, by weight, of at least one crosslinker molecule, wherein the difference in the glass transition temperatures (T_(g)) of the different polymers is at least 10° C., and b) 30-50%, by weight, of at least one polyfunctional (meth)acrylate, and wherein the dispersion a) is subjected to physical and/or chemical deodorization.
 2. The dispersion of claim 1, wherein at least one principal monomer is selected from the group consisting of methyl methacrylate, n-butyl acrylate and ethylhexyl acrylate.
 3. The dispersion of claim 1, wherein at least one auxiliary monomer is selected from the group consisting of methacrylic acid, acrylic acid, acrylamide, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and 4-hydroxybutyl vinyl ether.
 4. The dispersion of claim 1, wherein at least one crosslinker molecule is selected from the group consisting of 1,4-butanediol diacrylate, allyl methacrylate, ethylene glycol (meth)acrylate, propylene glycol (meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,2-neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tetra(meth)acrylate and divinylbenzene.
 5. The dispersion of claim 1, wherein at least one polyfunctional (meth)acrylate b), is selected from the group consisting of trimethylolpropane triacrylate, and acrylates of ethoxylated and/or propoxylated trimethylolpropane or pentaerythritol.
 6. The dispersion of claim 1, wherein the polyfunctional (meth)acrylate b), is incorporated into the dispersion at a temperature above 40° C.
 7. The dispersion of claim 1, which is subjected to chemical deodorization with an oxidizing and reducing agent.
 8. The dispersion of claim 7, wherein the reducing agent is used as a whole amount in excess over the oxidizing agent.
 9. The dispersion of claim 7, wherein at least some of the reducing agent is added, following treatment with the oxidizing agent.
 10. A method of coating a substrate, comprising coating the substrate with the polymer dispersion as claimed in claim
 1. 11. An article obtained by coating a substrate with a polymer dispersion as claimed in claim
 1. 12. An article comprising a substrate and a coating formed from the polymer dispersion as claimed in claim
 1. 13. The dispersion of claim 2, wherein at least one auxiliary monomer is selected from the group consisting of methacrylic acid, acrylic acid, acrylamide, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and 4-hydroxybutyl vinyl ether.
 14. The dispersion of claim 13, wherein at least one crosslinker molecule is selected from the group consisting of 1,4-butanediol diacrylate, allyl methacrylate, ethylene glycol (meth)acrylate, propylene glycol (meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,2-ethylene glycol di(meth)acrylate, 1,2-neopentyl glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tetra(meth)acrylate and divinylbenzene.
 15. The dispersion of claim 14, wherein at least one polyfunctional (meth)acrylate b), is selected from the group consisting of trimethylolpropane triacrylate, and acrylates of ethoxylated and/or propoxylated trimethylolpropane or pentaerythritol.
 16. The dispersion of claim 15, which is subjected to chemical deodorization with an oxidizing and reducing agent.
 17. The dispersion of claim 8, wherein at least some of the reducing agent is added, following treatment with the oxidizing agent.
 18. A method of coating a substrate, comprising coating the substrate with the polymer dispersion as claimed in claim
 16. 19. An article obtained by coating a substrate with a polymer dispersion as claimed in claim
 16. 20. An article comprising a substrate and a coating formed from the polymer dispersion as claimed in claim
 16. 